Onychomycosis is a fungal infection of the fingernails and toenails that results in thickening, discoloration, splitting of the nails and lifting of the nails from the nail bed. The disease is caused by dermophytes and has a high incidence within the general population, especially among older individuals. Onychomycosis is most commonly caused by Trichophyton rubrum (T. rubrum), Trichophyton mentagrophytes (T. mentagrophytes), and Epidermophyton floccusum (E. floccusum). Onychomycosis due to nondermatophytes is usually caused by Candida species, such as Candida albicans, and is more likely to cause invasive nail disease in fingernails than in toenails of immunocompetent individuals.
Rates of onychomycosis vary with the population considered. A recent study of the general United States population revealed a prevalence of 2% to 3%, while a study reported in Finland reported a rate of 13% (Elewski et. al., J. Am. Acad. Dermatol. 2000; 42(1)(Pt 1): 1-20, and Heikkila et. al., Br. J. Dermatol. 1995; 133(5): 699-703). Onychomycosis may affect up to about 15% of persons between the ages of 40 and 60 years (Kepka et. al. U.S. Patent Pub. No. 2006/0067898).
Terbinafine is an antimycotic currently indicated as an oral therapy for the treatment of onychomycosis (Lamisil™, Novartis International AG, Basel, Switzerland). Other treatment options including chemical or surgical removal of the infected nail(s) can lead to nail bed shrinkage and dorsal dislocation of the nail bed.
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